BUBBLES at a glance

BUBBLES is a SESAR2020 Exploratory Research project that aims to formulate and validate a Concept of Operations (ConOps ) for a U-space advanced (U3) ‘Separation Management service’, defining the basic blocks from which this service will be built and describing how they must be assembled and operated.

31 Oct 2020

The BUBBLES approach

The BUBBLES separation management ConOps involves the definition of a conflict horizon, separation modes, separation minima and the predetermined separator for all the hazards expected in the area of operation. The BUBBLES ConOps are operation-centric and risk-based. Operation-centric because the definition of separation modes and minima, as well as that of the conflict horizon and the designation of a predetermined separator will depend on the actual operational conditions. Risk-based because they also depend on the level of risk assessed using standard methodologies. The particularities of the operational environment will be captured in an Operational Services and Environment Description (OSED) that will support the development of Safety and Performance Requirements (SPR) and interoperability requirements (INTEROP) for the separation management service itself as well as for those U-space services and systems it relies on. The figure below outlines the procedure that BUBBLES is going to use to define the OSED and to derive the SPR/INTEROP.

A large variety of missions can take place in a given airspace volume. BUBBLES will define a set of generic UAS ConOps representative of most UAS missions in a U3 environment (i.e. advanced applications, such as urban air mobility, relying on a cooperative environment with an enhanced information-sharing system to allow situation awareness at both strategic and tactical levels). The generic UAS ConOps will be detailed enough as to support Specific Operational Risk Assessment (SORA), but they will be mission agnostic. Moreover, the UAS ConOps will describe the operation of pairs of UAS so that the hazard of mid-air collisions between UAS can be taken into account. Once the Catalogue is defined, SORA assessments will be conducted for each ConOps, leading to a risk-based classification which will take into account the air and ground risk attached to the operational environment as well as the effect of the applied mitigations.

Then, BUBBLES will define a scenario representative of a particular airspace volume by aggregating the UAS ConOps and taking into account the traffic density corresponding to the expected operations and considering the U-space services available therein. For this scenario, the project will obtain the pair-wise separation minima and that should be applied between each UAS flying in order to guarantee a particular Target Level of Safety (TLS) expressed in terms of frequency of collisions. The algorithms that will assign the separation minima will be based on a combination of analytical techniques inspired by those used in manned aviation and Artificial Intelligence (AI) based algorithms trained using sets of mission-based sampled trajectories generated using an OpenAI-gym Multi-UAV environment. BUBBLES will also develop AI-based separation modes to maintain the separation minima.

Setting requirements

The separation minima and modes will be first derived considering an ideal performance of the U-space services and systems involved in the separation management. To take into account the actual performance of these services and systems, BUBBLES will define an OSED consisting of assumptions on the environment and on external services and systems supporting the separation management, as well as on a set of operational requirements. From this OSED, the project will derive functional requirements applying a Functional Requirement Assessment (FRA) and will conduct an Operational Performance Assessment (OPA) and an Operational Safety Assessment (OSA) to define performance and safety objectives leading to performance and safety requirements that will be expressed by means of a set of nominal and non-nominal performance metrics, as described by the figure below. Acceptance thresholds will also be defined for those metrics.

BUBBLES will apply the MEthoDology for the U-Space Safety Assessment (MEDUSA) developed by the SESAR2020 CORUS project on the base of SESAR Safety Reference Material (SRM) adopting a broader approach which addresses both the positive contribution of U-Space to aviation safety (success approach), as well as the effect of U-Space failures on the collision risk (failure approach). BUBBLES will use the MEDUSA success approach to conduct the FRA and the OPA and the MEDUSA failure approach to conduct the OSA. In addition to the OPA and the OSA, BUBBLES will apply an AI-based Separation Error Model (SEM) to account for the effect of nominal and non-nominal U-space services performance. The SEM will also take into account weaknesses due to non-realistic assumptions of existing models and lack of data to create realistic models in UAS scenarios.

BUBBLES will capture the definition of generic OSEDs, as well as the SPR requirements derived by applying MEDUSA and the SEM to them in an OSED/SPR/INTEROP document. Moreover, BUBBLES will elaborate guidelines to apply the methodology developed by the project to local environments, providing guidance on how to set requirement values appropriate to the local system, how to evaluate the actual system performance and how to account for the effect of local system variations on BUBBLES assumptions.

The compliance with the thresholds set up in the SPR for the nominal and non-nominal metrics derived from the performance and safety objectives and requirements must be monitored so that the separation management service can adapt the applicable separation minima and modes to the actual performance of the U-space services and systems supporting it. To this end, BUBBLES will define methods to compute the performance metrics and will propose a functional description of a tool to demonstrate compliance with the applicable thresholds.

Validating the concept

BUBBLES will validate the separation management ConOps by means of a proof-of-concept which combines numerical (simulated) and experimental validation activities. First, the algorithms developed in by the project to compute the separation minima using trajectories obtained from a trajectory generator will be validated using a more realistic approach (see figure above). This validation will make use of the capability of the Indra UTM platform to reproduce UAS flights in a specific scenario given a flight plan. BUBBLES will develop a mock-up based on this platform to validate the separation management algorithm, the separation error model and the performance monitoring tool.

On the other hand, the effectiveness of the modes proposed by BUBBLES to maintain the separation minima will be validated by means of test flights and using a software mock-up supported by the Indra UTM platform, as shown in the figure below. In this case, the input data will consist of sets of configuration parameters defining each test scenario. In both cases, the output data will consist of reports in alphanumeric or graphic format.